The present invention pertains to a construction for an internal combustion engine utilizing geared hypocycloid motion and, more particularly, to such an engine construction including improved assembly, load distribution, and adjustment features.
The principles of hypocycloid motion have long been applied to the design of internal combustion engines. The use of a hypocycloid gearing system provides straight line piston motion and a significant number of resultant advantages. These advantages include perfect engine balance (even in a single cylinder engine), elimination of a piston wrist pin and piston skirt, and an overall reduction in piston friction by the virtual elimination of piston side loading.
Basic hypocycloid design, utilizing a fixed internal ring gear which is engaged by a pinion gear mounted on the crankshaft, often results in undesirable gear loadings and may be particularly unsuitable for use in diesel engines and other supercharged engines. As a result, a myriad of designs have been proposed to provide modified gearing arrangements which still provide the basic hypocycloid motion, but better distribute the transmission of piston force to the crankshaft. Although many variations in gear arrangements are possible, two basic designs of modified hypocycloid engines have emerged. One utilizes a crankshaft with a heavy, large diameter eccentric on which is rotatably mounted a larger eccentric disc to carry the piston rod and the other utilizes a more conventional crankshaft construction having a smaller crankpin on which is rotatably mounted a moderately sized eccentric disc to carry the piston rod. Examples of the former construction are shown in U.S. Pat. No. 4,237,741. The large mass main eccentric, characteristic of this construction, introduces substantial weight problems, inherent in the large eccentric itself and in the similarly large counterweights which must be utilized to provide engine balance. This further results in practical limitations on the length of piston stroke. These problems are obviated in the alternate construction utilizing a small crankpin and eccentric disc, as shown, for example, in U.S. Pat. No. 3,563,222. However, this design introduces other problems. First of all, the need to assemble the eccentric disc, pinion gear and counterweights on the crankpin for rotation thereon requires a composite crankshaft construction or split pinion gear, connecting rod and eccentric disc which can be taken apart and reassembled. In addition, the piston force may result in unacceptably high loadings on the smaller crankpin.
Both basic designs of modified hypocycloid engines require the use of supplemental gearing arrangements which inherently introduce alignment problems as a result of gear backlash. The elimination of backlash by precise machining and assembly is impractical and, as a result, some means of adjusting the gearing after assembly is desirable.